Photographic products



United States Patent 3,155,515 PHQTOGRAPEHC PRODUCTS lack RichardCeleste, Westfield, and Abraham Bernard Cohen, Springfield, N.J.,assignors to E. I. du Pont de Nemours and Company, Wilmington, Det, acorporation of Delaware No Drawing. Filed Nov. 8, 1962, er. No. 236,41711 Claims. (Q1. 96-ltl'7) This invention relates to photography, andmore particularly to new photographic products useful therein.

The principal processes of photography are based on the use ofcolloid-silver halide emulsion layers. In the prior art processes alatent image is formed by imagewise exposure of a radiation-sensitivesilver halide emulsion layer. Silver halide bearing a latent image hasbeen developed to silver by selective reduction in these instances. 7

In the prior processes of photography the unreduced silver remainingafter development has been removed by silver halide solvents or renderedinsensitive or transparent by treatment with complexing agents. Optionalafter-treatments include intensification and reduction, toning andtinting. However, the primary or first step in image formation alwayshas been based on the selective reduction step.

It is an object of this invention to provide new photographic silverhalide compositions, photographic layers and photographic elementsbearing a layer of silver halide. Another object is to provide processesfor making these products. A further object is to provide such productswhich are adapted to more versatile processes for forming silver andother images and which are simple, dependable and give results equal inquality to the prior conventional methods. parent from the followingdescription of the invention.

The objects of this invention are realized by new silver halidecompositions in which an image may be formed, after exposure to actinicradiation, by imagewise solution of the silver halide. The residualsilver halide image may then be converted to silver, dyed or tonedimages.

The novel photographic compositions and silver halide layers of thisinvention comprise silver halide crystals which have been treated, insubstantially greater than fog inhibiting amounts, with a selectedN-acylamino thiophenol having at least one form which can be representedby the formula wherein R is a hydrocarbon radical and whose silver saltis less soluble in water than silver chloride. These compounds arecharacterized in that when admixed with an aqueous silver halidedispersion it protects the silver halide crystals to such an extent thatwhen a silver halide dispersion protected by said compound is treatedwith 10%, by weight, aqueous sodium thiosulfate, at least three timesthe amount of silver halide remains undissolved as in a similardispersion successively treated with aqueous sodium hypochlorite andaqueous sodium thiosulfate, after vigorous agitation of the dispersionsfor 30 seconds at 25 C. The dispersion so successively treated clears,whereas the other dispersion remains turbid.

Preferably, thesilver halide crystals are dispersed in a Water-permeableorganic colloid to form a light-sensitive photographic emulsion. Theselected thiophenol can be added to the silver halide emulsion while thelatter is in the liquid state or the emulsion may be coated on asuitable support and the resulting element bathed or impregnated with asolution, e.g., an alcoholic solution Still further objects will be ap-Patented Nov. 3, 1964 of the thiophenol. In the working examples below,the amount of thiophenol in the silver halide emulsion is from about 0.4to 25 g. per mole of silver halide but wider ranges of concentration canbe useful, depending upon the particular organic compound, the size andnature of the silver halide crystals, the presence of other materialswhich may partially cover the surface of the silver halide crystal, andupon Various other factors.

The gelatimsilver halide ratio is quite flexible varying from 3:1 to1:30 depending on the particular organic compound and application.

In one commercially practical aspect of the invention, the silver halideis present in much higher concentration than in conventional emulsionsand emulsion layers.

In an important use of the products of the invention, direct positiveimages are formed by a process which comprises (a) Exposing imagewise toactinic radiation a photo sensitive layer comprising silver halidecrystals treated with the organic compound as described above,

(b) Treating the exposed layer in a solution of a silver halide solventto remove soluble silver halide in the exposed image areas, thus forminga positive silver halide image, and i (c) Washing the resulting layers.

If desired, the silver halide image may be viewed directly, e.g., byprojection (if on a transparent support) or it may be intensified by i v(d) Converting the residual silver halide to silver by treatment in afogging developer, e.g., a high pH, 1-phenyl-4-methyl-3-pyrazolidone/hydroquinone developer containing iodideion or by fogging the emulsion by exposure to light and then treatingwith a silver halide reducing agent, e.g,, a conventional silver halidedeveloper, and

(e). Washing the developed layer to reveal a positive silver image inthe original non-exposed areas.

The imagewise solution of the exposed silver halide/ thiophenol stratummay be elfected by the silver halide solvents commonly used asphotographic fixing agents, e.g., sodium thiosulfate, sodiumthiocyanate, concentrated solutions of potassium bromide, etc. Reductionof the treated, residual silver halide may be accomplished by use of anychemical reducing agent capable of reducing silver ion to silver metal,e.g., hydroquinone, metol, sodium hydrosulfite and stannous chloride.The function of the reducing agent may be enhanced by modifying thesurface properties of the treated, residual silver halide crystals bymeans of alcohol, thiourea, potassium iodide, etc. The silver halideimage may be. toned, e.g., with sodium sulfide, sodium selenide, etc. Inaddition, color images may be obtained by developing the treated,residual silver halide with a primary aromatic amine color developingagent in the presence of a color coupling compound either in thedeveloping bath or previously incorporated in the emulsion.

Since a broad new photographic principle has been discovered, theapplicant does not wish to be limited to a narrow class of thiophenolswith which the. silver halide crystals may betreated in preparing thenovel compositions of this invention... Instead, a number of usefulcompounds will be shown in the exemplary disclosure-and astraightforward and relatively simple test will be described by whichone skilled in the art may readily determine whether or not other giventhiophenols will have utility in this invention. Essentially, the testconsists of two parts, Test A and Test B. In Test A, the candidatethiophenol must render a dispersion of silver halide crystals insolublein a silver halide solvent, i.e., an aqueous solution of sodiumthiosulfate, at some pH between 1 and 13. If the candidate compoundelfects the insolubility required of Test A, it must also, to meet therequirements of Test B by forming with said dispersion of silver halidecrystals a reaction product which, upon treatment with an aqueoussolution of sodium hypochlorite, becomes soluble when subsequentlytreated with aqueous sodium thiosulfate. The following practical testsare provided in further exemplification of the invention and includespecific concentrations of solutions, times, etc., so that suitableorganic compounds may be readily and positively identified.

TEST A A solution nearly saturated at 25 C. with a candidate organiccompound is prepared using ethanol, acetone, dimethyl formamide, wateror other suitable solvents. Depending on the solubility, a solutionconcentration from 0.01 to percent by weight is obtained. Twentyfive m1.of a silver chlorobromide dispersion containing mg. of silver halide(calculated as silver bromide), prepared as described below, is treatedwith small increments (i.e., about 0.1 to 0.2 m1. at a time) of the saidcandidate solution under safelight conditions (Wratten 1A red filter orequivalent) until the silver halide dispersion either is renderedinsoluble in 10% aqueous sodium thiosulfate or the candidate is foundnot to cause insolubilization. Generally insolubilization will occurupon the addition of 0.05 g. or less of said candidate compound,calculated as the pure compound. Compounds which must be used insubstantially greater quantities than this, e.g., 1-2 g. to effectinsolubilization are considered less preferred compounds. The silverhalide dispersion insolubility is determined by taking a 0.5 ml. portionof the silver halide dispersion (after each incremental addition of thecandidate organic compound), adding about 0.1 to 0.2 ml. of 10% aqueoussodium thiosulfate solution and observing the turbidity after seconds.

As a control, one should use 25 ml. of water to which small incrementsof the candidate solution are added. Half milliliter portions of thecontrol are treated in the same manner with the sodium thiosulfatesolution. The presence of visual turbidity relative to the control issufficient to satisfy the definition of insolubility in this test.

This test may be repeated for various pH increments from 1 to 13.Although there is some optimum pH value at which the test is mostsensitive, this is not a sharp maximum which must be precisely attained.Rather, it has been found that there is a fairly broad range of pHvalues (e.g. 2.0 to 3.0 pH units) over which the test has a satisfactorysensitivity. In practice, the silver halide dispersion might be testedwithout adjustment (e.g. at pH 5.0 to 7.0) and if insolubilizationoccurs here, Test A is completed. If there is no insolubilization, thetest is repeated at a higher pH (e.g., about pH 1l-13). If there isstill no insolubilization, the test is conducted with emulsion adjustedto a lower pH (e.g., about pH l3). Thus three different pH valuesrepresents a practical maximum number which must be investigated todetermine whether or not insolubilization will occur.

TEST B An organic compound capable of insolubilizing a silver halidedispersion according to Test A is now ready for the next test, whichagain will be conducted under safelight conditions. To the above silverhalide dispersion, there is added the minimum amount of a solution ofthe candidate organic compound found necessary for insolubilization.Half-milliliter samples of the dispersion containing 0.5 mg. AgBr or0.29. mg. Ag are placed in two test tubes. To one sample is added 0.5ml. of water; to the other is added 0.5 ml. of a 5% by weight aqueoussolution of sodium hypochlorite (containing 25 mg. sodium hypochlorite).Next, there is added to both samples, 1.0 ml. of an aqueous 10% byweight solution of sodium thiosulfate (containing 100 mg. sodiumhypochlorite). If, after standing for up to 30 seconds, the sampletreated with sodium hypochlorite clarifies (or Silver Halide DispersionPreparation-Dispersi0n I The silver halide dispersion disclosed in TestsA and B is prepared according to the following specifications. In redlight, 30 g. of photographic grade gelatin is soaked in 1100 ml. ofdistilled water for 10 minutes. The temperature is then raised to 120 F.and g. of solid ammonium chloride added. The mixture is stirred at F.and after the ammonium chloride is completely dissolved, a solution madeby diluting 500 ml. of 3 N silver nitrate With 2000 ml. of distilledwater is added while stirring the mixture for 5 seconds. This mixture isheld at 120 F. for 4 minutes with stirring, and then ml. of 3 N ammoniumbromide added (30 mole percent) in 10 seconds. The mixture is held anadditional 15 minutes at 120 F. with stirring and then cooled to 100 F.A mixture of 75 g. of the sodium salt of technical lauryl alcoholsulfate (a white powder) and 7 ml. of 3 N sulfuric acid was added in 10seconds to the silver chlorobromide, stirring continued for one minuteand then the mixture allowed to settle. The supernatant liquid isdecanted and replaced by 2000 ml. of distilled water containing 4 g. ofsodium chloride. This mixture is stirred for 5 minutes at 100 F.,allowed to settle and decanted again. Two hundred ml. of distilled wateris added to the silver halide curds and the temperature adjusted to 95F. This mixture is vigorously stirred for 10 minutes at 95 F. and thenthe pH adjusted to 61:0.1 with aqueous sodium hydroxide solution. Theredispersed emulsion is then analyzed for silver halide contentcalculated as silver bromide and a dispersion made by diluting theappropriate amount with distilled water such that the dispersioncontains 1 mg. calculated silver bromide per m1.

Particularly preferred N-acylaminothiophenols of the wherein R is ahydrocarbon radical, are those which form silver salts of the formula:

Among the useful silver salts of the above formula are those which areinsoluble in aqueous ammonium hydroxide at pH 12.

Dispersed crystals of silver halide, treated with an appropriate amountof a suitable N-acylaminothiophenol are affected by exposure of aportion of said crystals to actinic radiation, e.g., ultraviolet,visible, infrared, X- radiation, etc., to such an extent that at least20% of the less soluble crystals remain when 90% of the more solublecrystals dissolve when treated in 10% by weight aqueous sodiumthiosulfate solution. Generally, the presence of solubilizing groups inthe R portion of the above formula should be avoided in order thatreaction products with silver halide will be formed which willsignificantly reduce the solubility of silver halide grains in silverhalide solvents. There are exceptions to this rule, particularly in thecase of suitable compounds containing solubilizing groups which arecompensated for by the presence of insolubilizing groups, e.g., longchain alkyl groups. The chemical testing for selecting suitablecompounds has been found to give absolute correlation, i.e., organiccompounds which have been subjected to Test A and Test B have producedwithout exception when tested in actual photographic emulsions, the veryeffects predicted by said tests. Combinations of the compounds withvarious basic dyes, including various cyanine dyes, and Methylene Blue(Colour Index No. 922), Crystal Violet A0 (Colour Index No. 681) andRhodamine 6 mar .11

GDN Extra (Colour Index No. 752) have proven useful additions.

The silver halide need not be a combination of silver chloride andsilver bromide, but may be silver chloride, silver bromide and othermixed halide systems conventional in photographic practice, e.g., silverbromoiodide. While, for rapid processing, a high silver halide to hinderratio is preferred, more conventional ratios can also be used.

In place of part of the gelatin, other natural or syntheticwater-permeable organic colloid binding agents can be used and in somecases such binders can be used alone. Such agents includewater-permeable or water-soluble polyvinyl alcohol and its derivatives,e.g., partially hydrolyzed polyvinyl acetates, ethers and acetalscontaining a large number of intralinear CH CHOH groups, hydrolyzedinterpolymers of vinyl acetate and unsaturated addition polymerizablecompounds such as maleic anhydride, acrylic and methacrylic acid estersand styrene. Suitable such colloids of the last-mentioned type aredisclosed in US. Patents 2,276,322; 2,276,323 and 2,397,- 866. Theuseful polyvinyl acetals include polyvinyl acetaldehyde acetal,polyvinyl butyraldehyde acetal and polyvinyl sodium o-sulfobenzaldehydeacetal. Other useful colloid binding agents which can be used includethe poly-N-vinyllactams of Bolton US. Patent 2,495,918, variouspolysaccharides, e.g., dextran, dextrin, etc., the hydrophiliccopolymers in Shacklett US. Patent 2,833,- 650, hydrophilic celluloseethers and esters, and polymers of acrylic and methacrylic esters andamides. Also, it hasbeen found practical to treat silver halide layerson a base material in the essential absence of a binder, e.g., bychemical or vacuum deposition.

The emulsions may optionally contain any of the usual adjuvantscustomarily employed in silver halide systems so long as they do notinterfere with the adsorption and complexing action of the essentialingredient of the essential ingredient of the invention.

The emulsion can be coated on any suitable support, e.g., celluloseesters, cellulose mixed esters; superpolymers, e.g., polyvinyl chloride(co) vinyl acetate, polyvinyl acetals, butyrals; polystyrene;polyamides, e.g., polyhexarnethylene adipamide, polyesters, e.g.,polycarbonates, polyethylene terephthalate, polyethyleneterephthalate/isophthalate, esters formed by condensing terephthalicacid and its derivatives, e.g., dimethyl terephthalate with propyleneglycol, diethylene glycol, tetramethylene glycol,cyclohexane-l,4-dimethanol (hexahydro-p-xyiene dialcohol); paper, metal,glass, etc.

As disclosed earlier, the desirable concentration of the selectedorganic compound depends on many factors such as the size and solubilityof the organic compound, the nature of its reaction with silver halide,the size and nature of the silver halide crystals, thee presence ofother materials which may react with or be adsorbed to the surface ofthe silver halide, etc. In Example 1 below, a number of organiccompounds are disclosed which were tested in a dispersion of silverhalide crystals wherein the average grain size was 035 (micron) indiameter, therefore about 0.043 t in volume, assuming cubic grains. Thesilver halide comprised 70 mole percent silver chloride and 30 molepercent silver bromide, with a specific density of about 5.7 g./cc. or5.7 lgj The weight per individual crystal or grain is O.043p. 5.7 l()g./ =0.25 l0* g. Assuming a molecular weight of 157 for the mixedAgCl-AgBr crystals, and dividing this number by the weight per grain,gives 157 g./mole+0.25 g.=6.3 l0 grains/mole. The area of a cubic grainof 0.35 1. diameter=6 .35 =.74,u. which, multiplied by the 6.3 X10grains per mole, gives a molar surface area of 4.6 10 ;t or 4.6x 10square angstroms.

A particularly preferred thiophenol is 4-i-butyrylaminothiophenol.Assuming that a single molecule of this compound could occupy an area ofsquare angstrorns, it would require 1.5 l0 molecules to occupy a molarsurface area of silver halide. With a molecular weight of 195, thiswould require 1.5 10 l9o O.50 g.

to just cover the surface of one mole of the silver halide crystals. InExample I it required 210x10 g. of 4-ibutyrylaminothiophenol toinsolubilize 2.5 10- g. of silver halide of average molecular Weight157. Therefore according to experimental data (test tube results) itwould require of this thiophenol to insolubilize one mole of the silverhalide. More significantly, as disclosed in Example II in a photographicemulsion coated on a film base support, it was found that 0.4 g. of thesame thiopheno-l per mole of silver halide gave optimum results. Thiscompares more closely with the theoretically determined amount of4-i-butyrylaminothiophenol required to cover the silver halide surface.

Elements suitable for this novel process can also be prepared by bathinga photographic film in a solution of an appropriate acylaminothiophenol.in this embodiment, the silver halide crystals near the surface of thecoated emulsion stratum are in contact with a higher concentration ofthe thiophenol. Crystals farther from the surface, are treated with lessof this organic compound and, if the rate of diffusion is suflicientlyslow, there may be considerably less of the compound (even approachingzero) reacting with the lower silver halide crystals than with thesurface silver halide crystals. In such elements, satisfactory resultsmight be obtained with only a fraction, e.g., one-half, of the amount ofthe organic compound theoretically calculated as required to just coverthe surface of a mole of the silver halide crystals.

The N-acylaminothiophenols used in accordance with this invention can bemade by reacting the corresponding acid chloride with theaminothiophenol, e.g., p-aminothiophenol dissolved in pyridine by slowlyadding the acid chloride at a temperature between 5 C. and 10 C. withstirring and allowing the mixture to stand about 24 hours. The mixtureis then poured into 1 liter of crushed ice containing 250 m1.concentrated HCl and 250 ml. water, the mixture is stirred vigorously,allowed to stand for about 5-10 minutes to ripen the crystals, which arewashed with water until free of acid, dried and recrystallized frommethanol. Typical crystals have the melting points given in thefollowing tables.

The invention will be further illustrated by but is not intended to belimited to the following examples.

EXAMPLE I Tests A and B have been described earlier as procedureswhereby one can determine whether or not a given N-acylaminothiophenolis suitable for use according to the process of this invention. Some ofthe compounds which were indicated as suitable according to thescreening procedures of both tests, have been incorporated into actualphotographic coatings and good results have been obtained. Below thereare listed a number of thiophenols which were tested in this manner including one of the compounds which has been found to be inoperable. Theinoperable compound shown failed to produce the insolubility required ofTest A and was therefore not subjected to further testing. In order toeliminate the necessity for complete photographic experiments with eachand every compound screened according to Tests A and B, a simulatedphotographic test has been devised and is designated as Test C. The testis believed to be completely adequate in that any compound which isfound suitable according to the photoexposed to the lamp for up tominutes.

graphic test to be described in the next paragraph is also foundsuitable according to Tests A and B.

TEST C A 0.5 ml. portion of the insolubilized dispersion prepared inTest A under safelight conditions is placed in a 12 x 75 mm. Pyrex testtube three inches from a No. 2 reflectoflood lamp. This insolubilizeddispersion is A control consisting of another 0.5-ml. portion of theinsolubilized silver halide dispersion from Test A is taken undersafelight conditions. Two-tenths of a milliliter of 10% aqueous sodiumthiosulfate is added to each of the dispersion samples taken andcompared under safelight conditions. Any reduction in turbidity of thedispersion exposed to the reflectoflood lamp compared to the unexposedcontrol after treatment with aqueous sodium thiosulfate solution showsthat photosolubilization occurs.

Tests A, B and C were all conducted using Silver Halide Dispersion I,the preparation of which was given immediately following the descriptionof the procedure for Test B. To determine an approximate minimumconcentration of the organic compound required to effectinsolubilization of silver halide in the presence of an aqueous solutionof sodium thiosulfate, the qualitative procedure of Test A was repeatedin a more quantitative manner, using a ripened, washed and redispersed(but not chemically sensitized) gelatino-silver chlorobromide emulsionas described in Example I of assignees copending application, Nottorf,U.S. Serial No. 94,989, filed March 13, 1961. This emulsion isdesignated in the table below as Dispersion II and was made as follows:A lithographic emulsion having a silver halide composition of 30 molepercent AgBr and 70 mole percent AgCl and having grams of gelatinpresent per mole of silver halide for the steps of precipitation andripening was freed of unwanted, soluble, by-product salts by acoagulation and wash procedure as taught in Waller et al. US Patent2,489,341, wherein the silver halide and most of the gelatin werecoagulated by an anionic wetting agent, sodium lauryl sulfate, using anacid coagulation environment. Following the washing step, the emulsioncoagulate was redispersed in water together with 47 grams of additionalbulking gelatin.

N-Acylaminothiophenols of silver halide. This emulsion was applied at acoating Weight of 46 mg. of silver per square decimeter on 0.004 inchthick polyester photographic film base (with a sublayer to provideproper adhesion) as described in Example IV of Alles, U.S. Patent2,779,684. The coating, after imagewise exposure, showed a gerater rateof fixing in an 0.5 molar aqueous solution of sodium thiosulfate inexposed areas than in the unexposed areas so as to form a positivesilver halide image. Subsequent flashing to white light, followed bytreatment with a reducing agent (a conventional photographic developingsolution containing l-phenyl-4-methyl-3-pyrazolidone and hydroquinone),resulted in the formation of a positive image of metallic silver. Theoptical densities of completely unexposed areas and heavily exposedareas of the film, as determined using a Western Electric RA-l00CDensitorneter, were 1.11 and 0.05, respectively.

EXAMPLE III Optical Density C ompound Unexposed Exposedt-lsovalerylaminothio phen 0L 4-n-HexanoylaminothiophenoL4-n-Oetanoylaminothioplienol 4-Dodeeylarninothiophcnol4-[1-Naphthoylamino] thiophen 4-0yclohexanecarbonylalninothiop4-Trimethylacetylaminothiophenol The silver halide photosoluble elementsof this invention (litter from conventional silver halide emulsionscontaining antifogging agents in that the insolubilizing compounds usedin the photosoluble elements are present in substantially greater thanfog-inhibiting amounts. The

Test; Results with Dispersion I Gins. Corn pound to Insol- Meltingubilizte Dis- Compound Point, Insolubili- Chemical Photosolpersion 11 C.zation Test Solubilizaubilization Containing 25 A tion Test Test 0 mg.Silver B Halide 1. 4-Acetylarninothiophenol Insoluble 0. 00015 2.4-Isobutyrylarninothiophcnol. 0.0002 3. 4-Is0va1erylamin0thiophenoL0.0002 4. 4-nI-Iexanoylaminothiophenol 0.0002 5.4-!1-0etauoylaminothiophenol. 0.0002 6. 4-dodecanoylamiuothiophenoL. 0.0003 7. p-[Phthaloy1amin01-tlnopheno 0.002 8. p,-[Terephtl'|aloylamiuo]-thiop 0.002 9. 4-p-Nitrobenzoylamino1-thioplienol 0. 004 10.4-[l-Naphthaloyla1nino1-tl1ioplieno 0. 003 11.4-[p-Anisoylarninol-thiophenol 0. 004 12.4-Cyclohexanecarbonylaminotliiop 0. 0011 13.4-lrimethylacetylaminothiophenol ,do 0.0015 14.4-[p-n-A1nowbeuzoylamino]-thiophenol-. Solublem- EXAMPLE II An emulsionas described in Dispersion 11, Example I was redispersed in a 5% gelatinsolution which contained 47 g. gelatin per mole of the silver halide. ApH 6.0:.1 was maintained while dispersing 10 min. at F. The emulsion wasbrought to 2320 g. by addition of water and the temperature adjusted toF. Four-tenths of a gram of 4-i-butyrylaminothiophenol was added permole of silver halide from a 1% by weight ethanol solution. Chrome alumhardener was added and the emulsion was diluted with water to a totalweight of 2334 g. per mole latter amounts constitute the maximumquantity that provides low fog without serious loss in speed andphotographic quality. For this reason it is not practical to usephotosoluble elements in place of ordinary silver halide photographicmaterials. When photosoluhle elements are exposed and processednormally, development proseeds slowly and incompletely to give anegative silver image having much less speed and lower density. Inaddition, fixing is slower and may be incomplete for practical fixingtimes. Thus, photosoluble elements require longer conventionalprocessing times and give slower speed, in-

9 ferior quality images when compared to ordinary silver halidephotographic elements.

The novel photographic compositions of this invention have numerousadvantages. A primary advantage is the simplicity of their preparation.They can be exposed and processed to images under ordinary room lightconditions.

The photographic processes applicable to the compositions and elementsof the invention likewise have advantages over previously known systemsbased on selective reduction of exposed silver halide for forming eitherdirect positive or negative images without resorting to the specialefiiects and sensitizing procedures previously used for preparing suchimages. In addition, since image formation does not require selectivereduction, this present process is not limited to the use of certainphotographic developing agents but may be accomplished by using a widerange of reducing agents. Many such compounds are of very low cost andcan be used to form images of much higher covering power than customary,thus effecting important economies in processing, as well as greatlyincreasing the efliciency of the silver image with a resultant increasein sensitivity.

Another advantage of the compositions and elements of this invention isthat they may be processed to form silver halide or silver imageswithout the requirement of special equipment but instead conventionalequipment and apparatus can be used. A further advantage is that theprocesses can be carried out successfully by photographic techniciansand photographers of ordinary skill. A still further advantage is thatthe processes utilize conventional reducing agents, e.g., developers andfixing agents. Still additional advantages will be apparent from theabove description of the invention.

We claim:

1. A photographic silver halide emulsion before exposure to actinicradiation comprising silver halide crystals having associated therewithin substantially greater than fog-inhibiting amount a4-N-acylaminothiophenol, the silver salt of said thiophenol being oflower solubility in water than silver chloride and less soluble in 10%aqueous sodium thiosulfate than untreated silver halide crystals at apredetermined pH, said 4-N-acylaminothiophenol being present in such anamount, in terms of the ratio of its weight to the surface area of thesilver halide crystals, that when admixed in such ratio with an aqueoussilver chlorobromide dispersion, 70/30 mole percent, gelatin dispersioncontaining 0.29 mg. of Ag in ml., and said silver chlorobromidedispersion is treated with 10% by Weight aqueous sodium thiosulfate, sothat the resulting mixture contains 0.29 mg. of Ag and 100 mg. of sodiumthiosuliate, at least three times the amount of silver chlorobromideremains undissolved as compared with a similar dispersion successivelytreated with 5% by weight aqueous sodium hypochlorite and by weightaqueous sodium thiosulfate, so that the resulting mixture contains 0.29mg. of Ag, mg. of sodium hypochlorite and 100 mg. of sodium thiosuliate,after vigorous agitation of both dispersions for seconds at 25 C.

2. An emulsion according to claim 1 wherein the acyl radical in saidthiophenol is a saturated aliphatic acyl radical of 3 to 13 carbonatoms.

3. An emulsion according to claim 1 wherein the acyl radical in saidthiophenol is an aromatic acyl radical.

4. An emulsion according to claim 1 wherein the emulsion is a gelatinemulsion and said silver halide is silver chlorobromide.

5. An emulsion according to claim 1 wherein the emulsion is a gelatinemulsion and the silver halide is silver chlorobromide and thegelatin/silver halide ratio is 3:1 to 1:30, by weight.

6. A photographic element comprising a support bearing a layer of asilver halide emulsion before exposure to actinic radiation comprisingsilver halide crystals having associated therewith in substantiallygreater than foginhibiting amounts a 4-N-acylaminothiophenol, the silversalt of said thiophenol being of lower solubility in water than silverchloride and less soluble in 10% aqueous sodium thiosulfate thanuntreated silver halide crystals at a predetermined pH, said4-N-acylaminothiophenol being present in such an amount, in terms of theratio of its weight to the surface area of the silver halide crystals,that when admixed in such ratio with an aqueous silver chlorobromidedispersion, /30 mole percent, gelatin dispersion containing 0.29 mg. ofAg in /2 ml., and said silver chlorobromide dispersion is treated with10% by weight aqueous sodium thiosulfate, so that the resulting mixturecontains 0.29 mg. of Ag and mg. of sodium thiosulfate, at least threetimes the amount of silver chlorobromide remains undissolved as comparedwith a similar dispersion successively treated with 5% by weight aqueoussodium hypochlorite and 10% by weight aqueous sodium thiosulfate, sothat the resulting mixture contains 0.29 mg. of Ag, 25 mg. of sodiumhypochlorite and 100 mg. of sodium thiosulfate, after vigorousagitationof both dispersions for 30 seconds at 25 C.

7. An element according to claim 6 wherein said 4-N- acylaminothiophenolis 4-n-hexylaminothiophenol.

8. An element according to claim 6 wherein said 4-N- acylaminothiophenolis 4-n-dodecanoylaminothiophenol.

9. An element according to claim 6 wherein said 4-N- acylaminothiophenolis 4-11-octanoylaminothiophenol.

10. An element according to claim 6 wherein the emulsion is gelatinemulsion and the silver halide is silver chlorobromide.

11. An element according to claim 6 wherein the emulsion is gelatinemulsion and the silver halide is silver chlorobromide and thegelatin/silver halide ratio is 3:1 to 1:30, by weight.

References Cited in the file of this patent UNITED STATES PATENTS2,025,876 Lubs et al. Dec. 31, 1935 2,131,038 Brooker et al Sept. 27,1938 2,985,661 Hein et al May 23, 1961 3,046,130 Dersch et al. July 24,1962 3,063,837 Lassig et al Nov. 13, 1962 3,080,230 Haydn et al. Mar. 5,1963 OTHER REFERENCES Lankelma et al.: Journ. Am. Chem. Soc., vol. 53,No. 1, pages 309-313, January 1931.

Elderfield: Heterocyclic Compounds, vol. 5, publ. by I. Wiley, N.Y.,1957; pages 506-508 relied on.

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1. A PHOTOGRAPHIC SILVER HALIDE EMULSION BEFORE EXPOSURE TO ACTINICRADIATION COMPRISING SILVER HALIDE CRYSTALS HAVING ASSOCIATED THREWITHIN SUBSTANTIALLY GREATER THAN FOG-INHIBITING AMOUNT A4-N-ACYLAMINOTHIOPHENOL, THE SILVER SALT OF SAID THIOPHENOL BEING OFLOWER SOLUBILITY IN WATER THAN SILVER CHLORIDE AND LESS SOLUBLE IN 10%AQUEOUS SODIUM THIOSULFATE THAN UNTREATED SILVER HALIDE CRYSTALS AT APREDETERMINED PH, SAID 4-H-ACYLAMINOTHIOPHENOL BEING PRESENT IN SUCH ANAMOUNT IN TERMS OF THE RATIO OF ITS WEIGHT TO THE SURFACE AREA OF THESILVER HALIDE CRYSTALS, THAT WHEN ADMIXED IN SUCH RATIO WITH AN AQUEOUSSILVER CHLOROBROMIDE DISPERSION, 70/30 MOLE PERCENT, GELATIN DISPERSIONCONTAINING 0.29 MG. OF AG IN 1/2 ML., AND SAID SILVER CHLOROBROMIDEDISPERSION IS TREATED WITH 10% BY WEIGHT AQUEOUS SODIUM THIOSULFATE, SOTHAT THE RESULTING MIXTURE CONTAINS 0.29 MG. OF AG AND 100 MG. OF SODIUMTHIOSULFATE, AT LEAST THREE TIMES THE AMOUNT OF SILVER CHLOROBROMIDEREMAINS UNDISSOLVED AS COMPARED WITH A SIMILAR DISPERSION SUCCESSIVELYTREATED WITH 5% BY WEIGHT QUEOUS SODIUM HYPOCHLORITE AND 10% BY WEIGHTAQUEOUS SODIUM THIOSULFATE, SO THAT THE RESULTING MIXTURE CONTAINS 0.29MG. OF AG, 25 MG. OF SODIUM HYPOCHLORITE AND 100 MG. OF SODIUMTHIOSULFATE, AFTER VIGOROUS AGITATION OF BOTH DISPERSIONS FOR 30 SECONDSAT 25*C.